The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.
U.S. Pat. No. 3,165,296 (Drew) discloses an apparatus for raising and lowering stage drops. A movable support member is provided for supporting a stage drop. A head block such as a pulley having a plurality of grooves is mounted adjacent the top position of the stage drop. An arbor adapted to carry weight for counterbalancing the stage drop is disposed below the head block. A plurality of flexible supporting cables are disposed over the head block and connected at one end to the support member and at the other end to the arbor. A control cable is connected at each end to the arbor and means for supporting the control cables above and below the arbor are provided so that the arbor is moved in a downward direction when the control cable is moved in one direction and the arbor is moved in an upward direction when the control cable is moved in the other direction. An electric motor is coupled to the control cable. A source of energizing potential is connected to the motor through motor control means for controlling the motor to selectively raise and lower the arbor and thereby raise and lower the stage drop.
U.S. Pat. No. 5,711,713 (Krueger) discloses a modified theatrical counterweight apparatus in a double or single purchase counterweight system, which consists of a counterweight arbor carriage for holding a plurality of counterweights. The counterweights are stored on two elongate arbor bars, which when released will slide down into the counterweight arbor carriage. The counterweight arbor carriage when obtaining the proper amount of the counterweights will slide down the elongate arbor bars to raise a piece of scenery with a batten up from a stage, via lift lines and an operating line.